The present invention relates to magnetic recording media, and more particularly relates to perpendicular magnetic recording media having a patterned soft magnetic underlayer that reduces intersymbol and adjacent track interference.
Perpendicular magnetic recording systems have been developed for use in computer hard disk drives. A typical perpendicular recording head includes a trailing write pole, a leading return or opposing pole magnetically coupled to the write pole, and an electrically conductive magnetizing coil surrounding the yoke of the write pole. The bottom of the opposing pole has a surface area greatly exceeding the surface area of the tip of the write pole.
Conventional perpendicular recording media typically include a hard magnetic recording layer and a soft magnetic underlayer which provide a flux path from the trailing write pole to the leading opposing pole of the writer. To write to the magnetic recording media, the recording head is separated from the magnetic recording media by a distance known as the flying height. The magnetic recording media is moved past the recording head so that the recording head follows the tracks of the magnetic recording media, with the magnetic recording media first passing under the opposing pole and then passing under the write pole. Current is passed through the coil to create magnetic flux within the write pole. The magnetic flux passes from the write pole tip, through the hard magnetic recording track, into the soft underlayer, and across to the opposing pole.
Perpendicular recording designs have the potential to support much higher linear densities than conventional longitudinal designs, especially when a bilayer perpendicular media with a soft magnetic underlayer is used. Magnetization transitions on the bilayer recording disk are recorded by a trailing edge of the trailing pole and reproduce the shape of the trailing pole projection on the media plane. However, due to the change in skew angle as the recording head travels in an arc across the disk and possible misalignment of the write pole, this can result in unwanted side writing when a rectangular shaped write pole is used.
The underlayer used in perpendicular magnetic recording causes relative long-range intersymbol interference, both along the track and from track to track. The intersymbol interference effects are caused by a data dependent changes in the length of the magnetic return path from the reader through the underlayer and back through a much larger return pole area. For example, if the vertical domain orientation of the previously recorded data bits and the data bits on the adjacent tracks are all in the same direction as the data bit being read, then the surrounding domains may impede the flow of flux through the larger return pole. In this case, the sensed field by the reader would be lower in amplitude. This intersymbol and adjacent track interference may be a problem with traditional high density PRML recording codes and hence should be controlled.
One way to minimize the return path effect is to use a DC balanced code in which the number of up-pointing domains and the number of down-pointing domains are equal over some short distance such as 32 bits. This type of code is customarily used in CD recording. An example is the eight of fourteen modulation (EFM) code which uses 14 bits to encode a byte of data and another 3 bits to cause the code to be DC balanced. Such a code would make the magnetic data DC balanced over a 1 micron circle if the channel bit length were say 60 nm. The problem with DC balanced codes is that they result in a lower effective bit density as compared with PRML codes.
Unfortunately, DC balancing in the radial direction cannot adequately be addressed. The encoding can be DC balanced within a data record. However, the adjacent track spacing, the location of the gaps between data records, and the old information between tracks and in the gaps are not well controlled. For example, there is little side erasing in perpendicular recording. Hence, if the 6-sigma TMR is 30 percent of the track pitch, there will be large areas of old information that will cause the readback signals to be distorted even though the read back head does not pass directly over this data.
If the recording films are removed or made magnetically dead, e.g., by ion implantation between the tracks, the old information between tracks will be reduced. Further, if the recording films are removed or made dead where the inter-record gaps will occur, the old information interference from the gap will be reduced. The problem with removing the films is that one is left with a surface topology that may affect the ability of the recording head to fly on the surface. These known options require processing of an otherwise finished disk in order to apply the pattern. Therefore, there is a risk that the magnetic properties of the recording films or the flyability of the surface will be adversely affected.
A need therefore exists to pattern the substrate before the films are added in such a way that neither the magnetic properties of the recording films or the flyability of the surface are adversely affected. The present invention has been developed in view of the foregoing.
An aspect of the present invention is to provide a perpendicular magnetic recording media including means for reducing intersymbol interference between adjacent tracks of a magnetically hard recording layer of the recording media.
Another aspect of the present invention is to provide a perpendicular magnetic recording media comprising a substrate, a patterned magnetically soft underlayer on the substrate, and a magnetically hard recording layer over the patterned underlayer, wherein the patterned underlayer comprises discontinuities between adjacent tracks of the recording layer.
A further aspect of the present invention is to provide a method of making a perpendicular magnetic recording media. The method comprises the steps of providing a substrate, providing a patterned magnetically soft underlayer on the substrate, and depositing a magnetically hard recording layer over the patterned underlayer, wherein the patterned underlayer comprises discontinuities between adjacent tracks of the recording layer.
These and other aspects of the present invention will be more apparent from the following description.